JPH0284847A - Costas loop type demodulating system - Google Patents

Abstract

PURPOSE:To easily pull in frequency and to attain stable demodulation even when a transmission speed is low by providing a sweep/track control signal generating part, etc., and varying a range for the frequency locking. CONSTITUTION:When a phase state change signal (INIT signal), which is outputted when a phase state is changed, is inputted to a sweep/track control signal generating part 7, a sweep control signal is inputted to loop filter 5. As a result, a voltage control oscillator 6 goes to a sweep mode and the dislocation of phase difference sweeps -45 deg. to 45 deg.. A frequency locking range F is set large). When the range includes phase difference '0', a track control signal is outputted from the generating part 7 and the oscillator 6 cancels the sweep mode. Then, the phase difference is caused to be completely '0' on the basis phase deviation signal from a phase detecting circuit 4. When synchronization is completed, the 'F is changed to a value which is smaller than the value up to the present. Thus, even when the transmission speed is low, the frequency pull-in can be easily executed and the stable demodulation can be executed.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Conventional technology [Figures 4, 5, and 6 (a) to (C)] Problems to be solved by the invention To solve the problems Means (Fig. 1) Effect (Fig. 1) Embodiment (Figs. 2 and 3) Effects of the invention [Summary] Costas (ostas) that generates carrier wave (carrier) regeneration or clock regeneration based on baseband data
) Regarding the loop type demodulation method, the purpose is to make the range for frequency pull-in variable, so that even in the case of low transmission speeds, frequency pull-in can be easily performed, and stable demodulation is possible. A frequency pull-in auxiliary section that gives the voltage-controlled oscillator control signal output from the loop filter the required range for frequency pull-in sets the frequency pull-in auxiliary section based on the control signal from the sweep/track control signal generator. The frequency pull-in range to be added to the voltage-controlled oscillator control signal is set to be large when the voltage-controlled oscillator is in the sweep mode, and set to be small when the voltage-controlled oscillator is in the track mode.

[Industrial Application Field] The present invention relates to a Costas loop demodulation method that generates carrier wave (carrier) recovery or clock recovery based on baseband data.

In the case of synchronous detection, a circuit is required on the receiving side to reproduce a carrier wave that is in phase with the carrier wave component of the modulated input wave. An example of such a carrier regeneration circuit on the demodulation side is a Costas loop.

[Prior art] Figure 4 shows a four-phase P using the conventional Costas loop demodulation method.
This is a block diagram of the S Ka [m device. In the four-phase PSK demodulator shown in FIG. Furthermore 48MHz
After being filtered by a bandpass filter 22 and having its gain adjusted by a variable attenuator 23, the 900 hybrid 1
Then, the signal is divided into two systems with a 90° phase difference.

Each signal is processed by a mixer 2A; 2B, a band-limiting low-pass filter 3A: 3B, and an A/D converter 10A;
The signal is input to the carrier regeneration circuit CRC via the IOB.

The carrier regeneration circuit CRC has the functions of phase detection and loop filter, and the output of the loop filter portion is sent to the voltage controlled oscillator (VC) via the D/A converter 11.
o) s, and the output of the voltage controlled oscillator 6 is input to each mixer 2A, 2B.

In addition, 24 is a bit timing recovery (clock regeneration circuit), and the output from this clock regeneration circuit 24 is A.
The signal is input to the /D converter 10A and IOB.

By the way, as shown in FIG. 5, this carrier regeneration circuit CRC includes a 1-phase detection circuit 4 and an up/down counter 51 . In addition to the addition/subtraction circuit 52, a sweep/track control signal generation section 7. It has a ΔF setting circuit 8'.

Here, the 1-phase detection circuit 4 is an A/D converter 10A.

The up/down counter 51 receives the signals from the up/down control section 50 and detects the phase deviation of these signals. (Down
), and the addition/subtraction circuit 52 adds ΔF from the ΔF setting circuit 8' to the count value from the up/down counter 51.
(Frequency pull-in range unit) is added or subtracted.

The sweep/track control signal generator 7 also receives an INIT signal (this signal is output when the phase state changes), which is output from a phase uncertainty removal circuit in an error correction circuit (FEC) that corrects errors in reproduced data. When receiving a phase state change signal), sweep
The up/down control unit 5 sends a control signal to perform the
0 and when the INIT signal is not input,
A control signal for track (Track: sweep stop) is input to the up/down control section 50. When the up/down control section 50 receives the sweep control signal from the sweep/track control signal generation section 7, it starts the up/down control signal. /The down counter 51 continues to count up or down, and the sweep/track control signal generator 7
When a track control signal is received from the phase detection circuit 4, the up/down counter 51 is controlled up/down based on the deviation information from the phase detection circuit 4.

Furthermore, the ΔF setting circuit 8' has an up/down counter S
The required range Δ for frequency pull-in to the count value from 1
It is given an F.

The reason why ΔF is given in this manner is that only one point can be specified using only the count value of the up/down counter 51, and therefore the frequency cannot be pulled in by the voltage controlled oscillator 6.

With this configuration, when synchronization is lost, for example, the INIT signal is input to the sweep/track control signal generator 7, and the sweep/track control signal is output from the sweep/track control signal generator 7. It is input to the down control section 50.

As a result, the up/down counter 51 continues to count up or down, and as a result, the count value increases or decreases in one direction. Then, a required ΔF is added or subtracted from this count value to control the voltage controlled oscillator 6 within a certain range. As a result, the phase difference shift sweeps between -45° and 45° [
Refer to FIG. 6(a)], and as shown in FIG. 6(b), when the range including the phase difference O is reached, a track control signal is output from the sweep/track control signal generating section 7. The up/down control unit 5° outputs an up/down control signal based on the phase deviation signal from the phase detection circuit 4 to the up/down counter 51, so that the count value of the up/down counter 51 changes according to this up/down control. Up/down depending on the signal, one phase difference completely O
[See Figure 6 (Q)].

[Problem M to be solved by the invention] By the way, when dealing with low transmission speeds, ΔF
If it is not made small, cycle skips will increase and stable demodulation cannot be expected.

However, if ΔF is small, there is a risk that the phase 0 point will be passed between when the track state is detected and when the up/down counter 51 is released from the one-way control. There is a problem in that the system returns to the sweep state and is unable to shift to the track state, and as a result, the frequency pull-in does not work properly.

The present invention was made in view of these problems, and
The Costas loop type uses a Costas loop, which allows the range for frequency acquisition to be made variable, making it easy to acquire one frequency even in the case of low transmission speeds, and enabling stable demodulation. The purpose is to provide a demodulation method.

[Means to solve the problem] FIG. 1 is a block diagram of the principle of the present invention.

As shown in FIG. 1, in the case of the present invention as well, each of the input signal lines divided into two systems by the 90° hybrid 1 is connected to mixers 2A and 2B.

A low-pass filter 3A:3B is provided to receive the output from the mixer 2A:2B, and each low-pass filter 3A
, 3B is output from the synchronous detection circuit 4, this deviation output is fed back to the voltage controlled oscillator 6 via the loop filter 5, and the output from the voltage controlled oscillator 6 is input to each mixer 2A, 2B. This is about the Costas loop demodulation method.

Further, 7 is a sweep/track control signal generation section, and this sweep/track control signal generation section 7 receives a phase state change signal (INIT signal) detected from the demodulated output and output when the phase state changes. Then, a sweep control signal for putting the voltage controlled oscillator 6 in the sweep mode is sent to the loop filter 5, and when the phase change signal is no longer input, a track control signal for putting the voltage controlled oscillator 6 in the track mode is sent to the loop filter 5. 5.

Further, reference numeral 8 denotes a frequency pull-in auxiliary unit, and this frequency pull-in auxiliary unit 8 gives a required range ΔF for frequency pull-in to the voltage-controlled oscillator control signal output from the loop filter 5, and this ΔF is variable. It is now possible to do so. That is, based on the control signal from the sweep/track control signal generation section 7, the frequency pull-in assisting section 8 sets ΔF set by the frequency pull-in assisting section 8 to a large value when the voltage controlled oscillator 6 is in the sweep mode. However, when the voltage controlled oscillator 6 is in the track mode, it is configured to be set small.

[Function] With this configuration, if the synchronization is lost, for example, the INIT signal is input to the sweep/track control signal generator 7, so the sweep/track control signal generator 7 outputs the sweep control signal. The signal is input to loop filter 5. This causes the voltage controlled oscillator 6 to enter the sweep mode, and the phase difference sweeps between 145° and 45°. ΔF at this time is set large.

Then, when the range includes a phase difference of 0, a track control signal is output from the sweep/track control signal generator 7, so the voltage controlled oscillator 6 cancels the sweep mode and outputs the phase deviation signal from the phase detection circuit 4. Based on this, the phase difference is completely set to 0.

When one phase difference becomes Q and synchronization is completed, ΔF is changed to a smaller value than before.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of a four-phase PSK demodulator that employs a Costas loop demodulation method as an embodiment of the present invention.
The QPSK wave in the 0MHz band is frequency-converted by a frequency conversion circuit according to the signal from the synthesizer, and is further converted to 48M.
After being filtered with a Hz bandpass filter and the gain adjusted with a variable attenuator, at 90° hybrid 1,
The signal is divided into two systems with a 90° phase difference.

Then, each signal is processed by a mixer 2A; 2B, a band-limiting low-pass filter 3A; 3B, and an A/D converter 10A:
The signal is input to the carrier regeneration circuit CRC via the IOB.

The carrier recovery circuit CRC has the functions of one-phase detection and a loop filter, and the output of the loop filter portion is sent to the voltage controlled oscillator (VC) via the D/A converter 11.
O) 6, and the output of the voltage controlled oscillator 6 is input to each mixer 2A, 2B.

By the way, this carrier regeneration circuit CRC includes an up/down control section 50. which constitutes the phase detection circuit 4 and the loop filter. Up/down counter 51, addition/subtraction circuit 5
In addition to 7.2, a sweep/track control signal generator 7. Δ
F variable circuit 8. It has a protection circuit 9.

Here, phase detection circuit 4. Up/down control section・50
．． Up/down counter 51. Since the addition/subtraction circuit 52 is the same as the conventional one, its explanation will be omitted.

Further, when the sweep/track control signal generating section 7 receives an INIT signal (phase state change signal) output from a phase uncertainty removal circuit in an error correction circuit (FEC) that corrects errors in reproduced data, the sweep/track control signal generating section 7 Control signal up/
When the INIT signal is not input to the down control section 50, the track control signal is input to the up/down control section 50. A timing chart of the input/output signals is shown in FIG. ) ~ (, Q).

Further, the ΔF variable circuit 8 has an up/down counter 5
The required range Δ for frequency pull-in to the count value from 1
This ΔF variable circuit 8 can further change the value of ΔF. That is, the ΔF variable circuit 8 adjusts the ΔF set by the ΔF variable circuit 8 based on the control signal from the sweep/track control signal generator 7.
is set large when the voltage controlled oscillator 6 is in the sweep mode, and set small when the voltage controlled oscillator 6 is in the track mode.

Furthermore, even if the control signal from the sweep/track control signal generating section 7 enters the sweep mode, the protection circuit 9 remains in the sweep mode for a while (during the time period from when the track state is entered until the phase difference is completely pulled into the O state). is for prohibiting the reduction of ΔF. Therefore, even if the vehicle enters the track state, if it shifts to the sweep state again within the time required to reduce ΔF, ΔF will not be changed.

Note that when the sweep state is entered after reducing ΔF, the protection circuit 9 issues an instruction to increase ΔF again through the ΔF variable circuit 8.

Due to the above configuration, for example, if synchronization is lost,
Since the INIT signal is input to the sweep/track control signal generation section 7, the sweep control signal is input from the sweep/track control signal generation section 7 to the up/down control section 5.
Input to 0. This causes up/down counter 5
1 continues to count up or count down, and as a result, the count value increases or decreases in one direction.

Then, a required ΔF is added or subtracted from this count value to control the voltage controlled oscillator 6 within a certain range.

As a result, the phase difference shift sweeps between -45° and 45° [see FIG. 6(a)]. ΔF at this time is set large.

Then, as shown in FIG. 6(b), when the range including the phase difference O is reached, a track control signal is outputted from the sweep/track control signal generating section 7, so the up/down control section 50 performs phase detection. An up/down control signal based on the phase deviation signal from circuit 4 is output to up/down counter 51.

As a result, the count value of the up/down counter 51 goes up/down depending on this up/down control signal.
The phase difference is completely set to O [see Fig. 6 (Q)], and synchronization is completed when the phase difference becomes O [not immediately after the track state is detected; see Fig. 3 (a)] and ΔF
will be changed to a smaller value than before.

Note that when the sweep state is entered after reducing ΔF, ΔF is again set large by the ΔF variable circuit 8 in response to an instruction from the protection circuit 9.

In this way, ΔF is increased during the sweep, so
Up/down counter 5 after detecting track status
While releasing the unidirectional control of 1 up/down, there is no risk of passing the phase 0 point, which allows for a successful transition to the track state, and thus a successful frequency pull-in, and the phase difference becomes 0. After that, ΔF is reduced, so even when dealing with low transmission speeds,
There is no increase in cycle skips, and stable demodulation can be expected.

[Effects of the Invention] As detailed above, according to the Costas loop demodulation method of the present invention, the voltage controlled oscillator control set by the frequency pull-in auxiliary unit is performed based on the control signal from the sweep/track control signal generation unit. The frequency pull range to be added to the signal is configured to be set large when the voltage controlled oscillator is in sweep mode, and set small when the voltage controlled oscillator is in track mode, so the transmission speed can be increased. Even when the frequency is low, there are advantages in that frequency pull-in can be easily performed and stable demodulation can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a timing chart showing input/output waveforms of the sweep/track control signal generator, and Fig. 4 is a block diagram showing the principle of the present invention. FIG. 5 is a block diagram of a 4-phase PSK demodulator, FIG. 5 is a block diagram showing a conventional example, and FIGS. 6(a) to 6(,) are diagrams explaining the sweep/track control process. In the figure, 1 is a 90" hybrid. 2A, 2A are mixer 3A, 3B is a low-pass filter. 4 is a phase detection circuit. 5 is a loop filter, 6 is a voltage controlled oscillator (VCO). 7 is a sweep/track control signal generator. , 8 is a ΔF variable circuit (frequency pull-in auxiliary part). 9 is a protection circuit, 10A and IOB are A/D converters. 11 is a D/A converter, 20 is a synthesizer 21 is a frequency conversion circuit, and 22 is a band pass filter. , 23 is a variable attenuator, 24 is a bit timing recovery (clock regeneration circuit), 50 is an up/down control section, 51 is an up/down counter, 52 is an addition/subtraction circuit, and CRC is a carrier regeneration circuit.

Claims (1)

[Claims] Each of the input signal lines divided into two systems is provided with a mixer (2A; 2B) and a low-pass filter (3A; 3B) that receives the output from the mixer (2A; 2B), The deviation output between each low-pass filter (3A, 3B) is sent to the voltage controlled oscillator (6) via the loop filter (5).
In the Costas loop demodulation method, which feeds back to the voltage controlled oscillator (6) and inputs the output from the voltage controlled oscillator (6) to each mixer (2A, 2B), the phase state detected from the demodulated output and output when the phase state changes. When a change signal is input, the voltage controlled oscillator (
6) to the loop filter (5), and when the phase state change signal is no longer input, a track control signal to put the voltage controlled oscillator (6) into the track mode. a sweep/track control signal generator (
7), and a frequency pull-in assisting section (8) that provides a required range (ΔF) for frequency pull-in to the voltage controlled oscillator control signal output from the loop filter (5), and the frequency pull-in assisting section (8) is provided. A section (8) determines the frequency pull-in range (ΔF )of,
Costas loop type, characterized in that the voltage controlled oscillator (6) is configured to be set large when it is in a sweep mode, and set small when the voltage controlled oscillator (6) is in a track mode. Demodulation method.